diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index a593d0e50d..77d2c116db 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -3872,7 +3872,7 @@ static int process_signal(sd_event *e, struct signal_data *d, uint32_t events, i
                         return -EIO;
 
                 if (_unlikely_(!SIGNAL_VALID(si.ssi_signo)))
-                        return -EINVAL;
+                        return -EIO;
 
                 if (e->signal_sources)
                         s = e->signal_sources[si.ssi_signo];